C++学习笔记 三

数组，结构体与类
数组的声明：

int list[5];

数组初始化时可以一次性赋值；如果不在初始化时一次性赋值，只能一个一个赋值了；
#include 
using namespace std;
int main() {
    int a[10]= {1,2,3,4,5,6,7,8,9,0};
    for (int i = 0; i < 10; ++i) {
        cout << a[i] < 
陷阱:数组的索引始终是从0开始的，同一数组的元素类型是一样的。
 陷阱：数组越界导致程序错误;
 
c++中数组也是可以作为形参的，而c语言中则是不可以的；
 
#include 
using namespace std;
void test(int a[],int size);
int main() {
    int a[10]= {1,2,3,4,5,6,7,8,9,0};
    test(a,10);
    return 0;
}

void test(int a[],int size)
{
    for (int i = 0; i < size; ++i) {
        cout << a[i] < 
数组参数与引用参数相似，在函数中改变数组形参也会影响到函数外的数组；
 在使用数组参数是，一般还要传出一个int型变量来存储数组的大小fd
 
#include 
using namespace std;
void test(int a[],int size);
int main() {
    int a[10]= {1,2,3,4,5,6,7,8,9,0};
    test(a,10);
    for (int i = 0; i < 10; ++i) {
        cout << a[i] << endl;
    }
    return 0;
}

void test(int a[],int size)
{
    for (int i = 0; i < size; ++i) {
        a[i] =a[i] + 1;
    }
}
 
数组的查询
 
#include 
using namespace std;
const int mun = 20;

void fill(int a[],int size,int &number_new);
void search(int a[],int number_new,int b);
void check(int &b);
int main() {
    int new_number,a[mun],b;
    fill(a,mun,new_number);
    cout << new_number << endl;
    for (int i = 0; i < new_number; ++i) {
        cout << a[i] << endl;
    }
    cout << "请输入你所要搜素的数字：";
    cin >> b;
    search(a,new_number,b);
    return 0;
}

void fill(int a[],int size,int &number_new)
{
    int count,b,c;
    cout << "请输入20个数字" << endl << "当你向停止输入时，请输入一个负数" << endl;
    do
    {        
        cin >> b;
        a[count] = b;
        count ++;
    }while((count < size)&&(b > 0));
    number_new = count;
}

void search(int a[],int number_new,int b)
{
    for (int i = 0; i < number_new; ++i) {
        if(a[i] == b)
        {
            cout << "寻找到目标:" << a[i]  << endl;
            return;
        }
    }
    cout << "很遗憾，我们没有找到你所需要的目标." << endl;
}
 
测试，通过测试发现当你输入多余的输入项，会占用之后的输入项；
 
#include 
using namespace std;
const int mun = 2;
void test(int a[],int size);
int main() {
    int a[mun],b;
    test(a,mun);
    cin >> b;
    cout << b;
    return 0;
}

void test(int a[],int size)
{
    int count,b;
    do
    {
        cin >> b;
        a[count] = b;
        count ++;
        cout << "q" << endl;
    }
    while(count < size && b > 0);
}
 
排序：
 使用冒泡排序时要记住：冒泡排序是需要嵌套循环的：
 
#include 
using namespace std;
const int mun = 20;

void fill(int a[],int size,int &number_new);
void sort(int a[],int &number_new);
int main() {
    int new_number,a[mun],b;
    fill(a,mun,new_number);
    cout << new_number << endl;
    for (int i = 0; i < new_number; ++i) {
        cout << a[i] << endl;
    }
    sort(a,new_number);
    for (int i = 0; i < new_number; ++i) {
        cout << a[i]<< endl;
    }
    return 0;
}

void fill(int a[],int size,int &number_new)
{
    int count,b,c;
    cout << "请输入20个数字" << endl << "当你向停止输入时，请输入一个负数" << endl;
    cin >> b;
    do
    {
        a[count] = b;
        count ++;
        cin >> b;
    }while((count < size)&&(b > 0));
    number_new = count;
}

void sort(int a[],int &number_new)
{
    int b,temp;
    cout << "请选择排序方式：n升序 ————1n降序————2";
    cin >> b;
    if(b == 1)
    {
        for (int i = 0; i < number_new -1; ++i) {
            for (int i = 0; i < number_new - 1; ++i) {
                if (a[i] > a[i + 1]) {
                    temp = a[i];
                    a[i] = a[i + 1];
                    a[i + 1] = temp;
                } else { ;
                }
            }
        }
    }
    else if(b == 2)
    {
        for (int i = 0; i < number_new -1; ++i) {
            for (int i = 0; i < number_new - 1; ++i) {
                if (a[i] < a[i + 1]) {
                    temp = a[i];
                    a[i] = a[i + 1];
                    a[i + 1] = temp;
                } else { ;
                }
            }
        }
    }
    else
    {
        cout << "输入错误，请重新输入。n";
    }
}
 
选择排列
 
#include 
using namespace std;
const int mun = 20;

void fill(int a[],int size,int &number_new);
void sort(int a[],int &number_new);
int main() {
    int new_number,a[mun],b;
    fill(a,mun,new_number);
    cout << new_number << endl;
    for (int i = 0; i < new_number; ++i) {
        cout << a[i] << endl;
    }
    sort(a,new_number);
    for (int i = 0; i < new_number; ++i) {
        cout << a[i]<< endl;
    }
    return 0;
}

void fill(int a[],int size,int &number_new)
{
    int count,b,c;
    cout << "请输入20个数字" << endl << "当你向停止输入时，请输入一个负数" << endl;
    cin >> b;
    do
    {
        a[count] = b;
        count ++;
        cin >> b;
    }while((count < size)&&(b > 0));
    number_new = count;
}

void sort(int a[],int &number_new)
{
    int b,temp,pos;
    cout << "请选择排序方式：n升序 ————1n降序————2";
    cin >> b;
    if(b == 1)
    {
        for (int i = 0; i < number_new -1; ++i) {
            pos = 0;
            for (int i = 0; i < number_new - 1 -i; ++i) {
                if (a[pos] < a[i + 1]) {
                    pos = i + 1;
                }
                if (pos != number_new-1)
                {
                    temp = a[pos];
                    a[pos] = a[number_new -1 -i];
                    a[number_new -1 -i] = temp;
                }
            }
        }
    }
    else if(b == 2)
    {
        for (int i = 0; i < number_new -1; ++i) {
            for (int i = 0; i < number_new - 1; ++i) {
                if (a[i] < a[i + 1]) {
                    temp = a[i];
                    a[i] = a[i + 1];
                    a[i + 1] = temp;
                } else { ;
                }
            }
        }
    }
    else
    {
        cout << "输入错误，请重新输入。n";
    }
}
 
多维数组
 赋值与显示：
 
#include 
#include 
using namespace std;
int main() {
    int a[30][100];
    srand(90);
    for (int i = 0; i < 30; ++i) {
        for (int j = 0; j < 100; ++j) {
            a[i][j] = rand()/1001;
        }
    }
    for (int i = 0; i < 30; ++i) {
        cout << endl;
        for (int j = 0; j < 100; ++j) {
            cout << a[i][j] <<"t";
        }
    }
    return 0;
}
 
结构体：
 结构体可以看作没有任何函数的对象；
 类则是包含函数与变量的对象；
 
#include 
using namespace std;
struct students
{
    int id;
    short sex;
    char age;
};
int main() {
    struct students st = {12,1,'q'};
    cout << st.age << endl << st.sex << endl < 
复合结构体
 
#include 
using namespace std;
struct students
{
    int id;
    short sex;
    char age;
};
struct people
{
    int name;
    struct students st1;
};
int main() {
    struct people st = {12,1,2,'q'};
    cout << st.name << endl << st.st1.id << endl < 
类
 
#include 
using namespace std;

class test
{
public:
    void show();
    int test_a;
    int test_b;
};
int main() {
    class test ts1;
    ts1.test_a = 1;
    ts1.test_b = 2;
    cout << ts1.test_a  <<"t" < 
"::"被称为作用域运算符;他前面的类名被成为类型限定语
 点运算符与作用域运算符都是用于表明成员所属于那个对象或类
 
抽线数据类型：数据类型的值以及相关操作对程序员不可见
 通过类隐藏成员函数或数据，称为信息隐藏，数据抽象，封装
 
公有（public）成员与私有（private）成员：
 类一旦私有化，私有成员变量只能在成员函数的定义中，其他都是非法的
 
#include 
using namespace std;

class test
{
public:
    int show();
    void set_a();
    void set_b();
private:
    int a;
    int b;
};
int main() {
    class test ts;
    ts.set_a();
    ts.set_b();
    cout << ts.show();
    return 0;
}

int test::show()
{
    return a+b;
}

void test::set_a() {
    cout << "请输入一个加数,a:n";
    cin >> a;
}


void test::set_b() {
    cout << "请输入一个加数,b:n";
    cin >> b;
}